Heating apparatus for injection molding machines



Jan. 26, 1943. E. s. BlRD ETAL 2,309,496

HEATING APPARATUS FOR mmcrrron MOLDING MACHINES Filed March 2, 1959 s Sh eets-Sheet 2 Jrzwrzirz- [Fm/0 13:5170 Z. 6071 FNa/ s/z Greg gar: Smlfk Jan. 26, 1943. E. s. BIRD ETAL HEATING APPARATUS FOR INJECTION MOLDING MACHINES Filed March 2, 1939 3 Sheets-Sheet. 5

mm "IIII L I I I I i 37: llllllil' .lll l||||\1\\ L J an Q N QM w fl irlm Patented Jan. 26, 1943 UNITED STATES PATENT OFFICE HEATING APPARATUS FOR INJECTION MOLDING MACHINES Application March 2, 1939, Serial No. 259,404

iclaims.

The present invention relates to inJection molding machines, particularly those employing material which is first rendered plastic by the application of heat, and is then injected into cooperating dies under pressure.

One object of the invention is to provide an improved heating apparatus of the above indicated character, wherein there is obtained a controlled heating of the thermoplastic mate rial. such as to insure the uniform flow of the material through the apparatus, and its injection into the dies at a temperature best suited for the molding operation. Since thermoplastic material of the type utilized in the apparatus usually exhibits a relatively narrow temperature range, in which it has the desired flow characteristics, the invention contemplates the automatic maintenance of diil'erent degrees of heat at diiferent stages in the conversion of the material from an unheated to a plastic condition, and in its flow through the apparatus to the dies. Such controlled heating substantially eliminates burning of the material either in the heater, or at the dies, and also makes it possible for the same heater to inject different quantities, or "shots," of plasticized material into diil'erent sized die cavities.

A further object of the invention is to provide a heating apparatus, wherein the passages through which the thermoplastic material moves, are so proportioned as to either gradually decrease, or remain constant, in cross sectional area, thereby making it possible to inject the plasticized material into the cooperating dies by the application of a moderately low pressure. Furthermore, these passages are formed with smooth continuous surfaces, with complete absence of pockets or angles in which the material may collect. Thus. there is assured an even measured movement of the entire mass of material in the heater for each operation of the injection plunger, so that when a change is made in the color or character of the thermoplastic material supplied to the machine, there will be no residual deposits of the previously used material, and the number of molded articles exhibiting a mixture of the two materials, will be reduced to a minimum.

The above and other advantageous features of the invention will hereinafter more fully appear from the following description, taken in connection with the accompanying drawings, in which:

Fig. 1 is a longitudinal sectional view, showing the construction of heating apparatus embodying the invention.

Fig. 2 is a transverse sectional view, along the line 2-2 of Fig. 1, looking in the direction of the arrows.

Fig. 3 is a transverse sectional view, along the line H of Fig. 1, looking in the direction of the arrows.

Fig. 4 is a diagrammatic view, illustrating the manner of obtaining controlled heating of the thermoplastic material as it passes through the apparatus.

Fig. 5 is a view partially in section and partially in side elevation, fllustratlng mechanism for feeding fresh thermoplastic material to the heater in charges of predetermined amount.

Like reference characters refer to like parts in the different figures.

Referring first to Fig. 1, the heating apparatus is shown mounted on a feed cylinder l, forming part of an iniection molding machine, such, for example, as shown and described in the copending application of Frederick W. McIntyre, Serial No. 168,987, filed October 14, 1937, since issued as Patent No. 2,246,414, dated June 1'7, 1941. The wall of the cylinder i provides an opening 2, to which thermoplastic material, preferabl in dry powdered form, is supplied by suitable mechanism adapted to deliver the material in charges of predetermined amount, as hereinafter more fully described with reference to Fig. 5.

The inside of the cylinder I is lined with a sleeve 3 of hardened metal, and provides an opening 4, in register with the opening 2 of cylinder i. An injection plunger 5 fits closely within the sleeve 3, and is movable back and forth therein, by means shown in Fig. 5. When the plunger I is moved to the retracted position, indicated in dotted lines, wherein its end is back of the cylinder opening 2, a given charge of thermoplastic material may enter the cylinder I, in front of the plunger 5. The plunger is annular in cross-section and by it forward movement in the cylinder i, forces thermoplastic material previously admitted, first through an alined annular passage 6, and then through converging channels I provided in a heater assembly mounted on the cylinder I.

For purposes of illustration, the heater assembly is shown as being formed in two parts 8 and 8, hereafter referred to as the heater body and nose, respectively, although obviously the passage and channels I may be otherwise formed. In order to support the heater assembly, the

forward end of the reed cylinder I provides a flange III. to which is attached the heater body 8. by means of a flange ii and bolts 42. The body I is generally in the form oi a hollow cylinder, having a recess U to receive the projecting end of the plumer sleeve I, with the bore l4 oi the body l exactly the same diameter as the outside diameter of the plunger 5.

The end of the body I opposite to the flange II, provides an annular seat 45, in which flts a cylindrical end portion it of the heater nose 8. The nose 9 provides a flange il, opposed to the end face of the body I and secured thereto by bolts II. The nose 8 carries a core ll extending rearwardly through the body 8, and making a close tit with the inside bore lia oi the plunger 5. The core I! is oi uniform diameter from its outer end to Just beyond the end of the plunger sleeve 8, from which point it gradually increases in diameter, to provide a frusto-conical portion 20. Therefore, the annular passage I thus formed within the heater body 8, is of gradually decreasing cross-sectional area, between the forward end of the plunger 5 and the nose 9.

Beyond the flange H, the nose 0 is tapered in form, and provides at its forward end, an opening 2|, for receiving a suitable nozzle 22 for engagement with the dies oi the associated injection molding machine, one of which is indicated in dotted lines at 23. Between the annular body passage 6 and the nozzle 22, the nose 8 provides the channels I, the divergent ends of which are in alinement with the passage 6, while their converging center lines meet at a common point, to form a single passage 24. The cross-sectional area of the passage 24 is materially less than the total cross-sectional areas of the combined channels 1, so that at the entrance to the nozzle 2|, the area available for the passage of the thermoplastic material is less than at any other point between the end of the in- .iection plunger 5 and the entrance to the nozzle 2|.

As best shown in Fig. 3, the divergent ends oi the channels I are flared outwardly. as indicated at 25, where the channels open into the annular passage 8. Consequently, the flared ends of adjacent channels are separated by sharp edges 28, disposed at the smaller ends of the annular passage 8, and there is no appreciable resistance to flow or plasticized material from the passage 4 into the channels I, as will later appear.

The nozzle 22 has a passage 21 therein, which at its inner end, corresponds in diameter to the passage 24 at the converging ends oi the channels I. The nozzle passage 21 gradually decreases in cross-section, to a neck 28, adjacent the discharge end oi the nozzle. The restricted area of the passage 21 at the neck 2|, is such that thermoplastic material injected into the die 23, will break away from the material further inside the nozzle, substantially at the neck 28 where the material has its smallest cross-section, and offers the least resistance to breaking loose.

The outside oi the heater body l is surrounded by one or more coils 29, of decreasing diameter in the direction of the nozzle 22, which. when connected to a source of alternating current, cause magnetic heating of that portion of the body surrounding the passage I, due to hysterisis effect within the body U. To this end, the body I is composed of magnetic material oi such a character as to produce a maximum hysterisis effect within the body. so that the heat is unitormly distributed throughout the body around the passage 8. In order to provide a return path for the magnetic flux outside of the coils 28, groups of laminations are arranged at intervals outside the coils. The particular construction of the body 8, coils 20 and laminations ll, in order to obtain a magnetic heating eilect within the body 8, forms no part 01' the present invention, but is more fully shown and described in the co-pending application 0! Graydon Smith and Albert Allen, Serial No. 258,494, filed February 25, 1939, since issued as Patent No. 2,226,447, dated December 24, 1940.

The nose 8 is similarly surrounded by one or more coils ii 01' decreasing diameter, and groups of laminations 32, so arranged as to cause magnetic heating from hysterisis eilect around channels I, when the coils ii are energized from an alternating current source. With the body 8 and nose 9 so related as to provide a continuous mass of magnetic material extending from the forward end of the injection plunger sleeve I to the nozzle 22, heating is continuous along the annular passage 6 and the converging channels I. Since thermoplastic material 0! the type utilized in the present apparatus usually exhibits a relatively narrow temperature range, in which it has the desired flow characteristics, the invention contemplates the automatic control of the degree of heat at diflerent portions of the heater, so as to insure conversion of the material from an unheated to a plastic condition, as well as the maintenance 01' the material in a properly plasticized condition for injection into th dies, always without danger oi burning the material.

For the purpose of obtaining automatic control of temperatures within the heater, the body 8 provides an opening 88, within which is received a thermo-couple 34, the lower end of which is located substantially mid-way oi the annular passage 6. The nose 9 similarly provides an opening 35, within which is received a thermo-couple 38, having its end located near the point where the channels I converge into the passage 24, adjacent to the nozzle II. The thermo-couples 34 and 36 are 0! any well-known type, such as to generate a given voltage, when subjected to a given degree of heat.

Referring now to Fig. 4, there is shown a wiring diagram of the electrical connections for the coils 29 and ii, respectively, together with an arrangement for utilizing the corresponding thermo-couples 34 and 36 to automatically maintain different temperatures of predetermined degree, within the body ii and the nose 9. In the control circuit, a source oi alternating current is indicated at 31, one side 0! which is adapted to be connected to one terminal of each of the coils 28 and II, through a switch 28 and a common conductor 39. The other terminals of the coils 29 and 3| are connected by conductors 40 and 4|, to potentiometer controllers 42 and 43, providing pairs of relatively movable contacts 44 and 46, respectively, with a common conductor 44, leading from the potentiometer controllers to the other side of the source 31. The terminals of the thermo-couple 34 in the body I, are connected by conductors 24a to the potentiometer 42 controlling the coils 28. while the terminals of the thermo-couple 26 in the nose I. are connected by conductors "a to the potentiometer 44 controlling the coils 3|.

The potentiomctcrs 42 and 42 are oi any wellreturn stroke. The yoke I! thus imparts mcveknowntype commercially available, and need not be described indetail herein, other than to state i that each potentiometer 42 or I is adapted to automatically control, through the contacts 44 or ll. the-connectionor disconnection oi'the corresponding coil I! or ll .to the source 11. Such automatic control is entirely dependent uponthe normal functioning of the potentiometer I r or 43, in response to the voltage generated by the thermo-couple It or it, when the temperature within the body [or nose 8 reaches a predetermined degree. with the control arrangement shown diagrammatically in Fig. 4. it is possible to so set thepotentiometers l2 and II, that a given temperature will be maintained within the body I, around the passage 8, while a lower or even higher temperature will he maintained within the nose I, aroundthe channels I. Obviously.- there will be gradations oi this temperature range between the nozzle II and the plunger end of the passage 6, the net result being, that there is a constantly maintained gradual reduction or increase in the temperature of the heater portions surrounding the thermoplastic material, as a predetermined charge thereof moves through the heater and is converted from a cold to a plasticized condition. r

As previously pointed out. the amount of material in each charge delivered to the cylinder l is controlledhy the mechanism shown in Fig. 5, wherein a hopper ll provides an opening communlcating with a charging cylinder 48. A piston bll is movable within the cylinder l9, so as to admit material from the hopper into the cylinder 4! through the opening It, When the piston is moved to its extreme right-hand position. The left-hand end oithe cylinder 49 opens into a chute 5|, extending downwardly into communiment directly to the piston head", so that the piston 50 is moved to its extreme right-hand position to expose the opening II and admit thermoplastic material into the cylinder II in front of the piston. When the plunger 5 starts its movement to the left, this movement is not imparted to the yoke 52 until the collar it strikes the yoke projection 54, as the plunger reaches that point in its injection stroke wherein it shuts oi! the cylinder opening 2. However, this movement of the yoke I! is not imparted to the feedcation with the opening] leading to the feed cylinder I, and left-hand movementof the pision is adapted to cause discharge of material into the chute II.

Reclprocatory, movement is imparted to the piston 50 from the injection plunger 5 through a yoke 52, slidably mounted above the plunger 5. The yoke 51 provides spaced operating projections 53 and 54. between which moves a collar 55 mounted on the plunger 5, so that as the plunger 5 is moved back and forth by a piston 55 operating in a fluid pressure cylinder 51, the

collar 55 imparts movement to the yoke 51 only when the plu er 5 nears the end of its operating stroke in either direction of movement. The yoke bl extends upwardly inside thepiston 50, and is adapted to engage a head 5! at the righthand end of the piston 50. whereby movement of the yoke 52 to the right is directly imparted to the piston 50.

For the purpose of. imparting left-hand movement of the yoke 52 to the piston 50, the yoke provides a rod 5! extending through a sleeve 6!. loosely carried by the piston head bl. The sleeve I is surrounded by a spring 6! between the head SI and a collarlLsothat normallynthe sleeve is maintained in the extended position shown. The rod ll extends freely through the sleeve 80, and is threaded to receive an adjustable stop 63. the position of which on the rod 59 determines the amount oi material in each charge delivered to the cylinder 1, for, feeding to the heater on each injection stroke of the plunger 5.

When the plunger 5 moves to the right, engagement oi the plunger collar 5! with the righthand yoke projection 53, moves the yoke 52 to the right as the plunger nears the end oi its ing piston ill until the stop I} on the rod 59 engages the collar I! on the sleeve Ill. when such engagement occurs, movement is imparted 'to the piston ill through the spring SI, and the degree of this movement will exactly determine the size of the charge of material that is fed into the heater for each inje'ctionstroke oi the plunger 5.

. By adjusting the position of the stop 63 on the rod Bl, with respect to the sleeve collar 62, the

left-hand limit of the movement oi the piston W in the cylinder 4!, can be closely set to determine just how much of the material in the cylinder 49 will be deliveredto the heater. Thus, shifting of the stop 8! to the right on the rod 59, will shorten the left-hand travel of the piston 50 in the cylinder ll to any desired extent, and so lirnlt the amount of material that is pushed over the edge of the chute I on the charging stroke of the piston 50. In this way, each charge can be made to substantially correspond to the size of each "shot" of plasticized material forced into the dies on the injection stroke of the plunger 5, since any decrease in the length oi the injection stroke of the plunger 5. due to filling of the dies, will correspondingly shorten the charging stroke of the piston I.

While it is contemplated that the cross-sectional area of the hopper opening [I shall remain unchanged for a given range oi injection shots.

the area of the opening can be varied, if desired. by shifting a plate I having the opening I8 therein. so as to alter the distance between one edge lilo of the opening and a bottom edge lid of the hopper 41. To this end, the plate 64 is movable beneath the hopper, by means of a screw shaft 85, mounted at the end of the cylinder 48 beyond the chute 5|. The threads on the shaft 55 cooperate with a. nut carried by the plate 51, so that by turning the shaft. the plate it can be moved longitudinally. Should it be desired to shut down the machine quickly, the shaft 65 can be readily turned to shift the plate 64 for enough to close the opening ll entirely. and thereby prevent any further discharge of material to the cylinder I.

After the plunger I has made several strokes. a suillcient quantity of the material from the hopper 41 will have been delivered to the heater to have completely tilled the. passage 6. channels I and the alined nozzle passages IQ and 21. This condition having once been obtained. subsequent operations of the plunger 5 will cause the injection of predetermined shots of plasticized material Into the dies, and the automatic control of the temperatures within the parts of the heater. is such as to assume. uniiormityoi molded product. Such uniformity results primarily from the functioning of the potentiometer controllers l2 and ll, whereby the temperatures are definitely maintained at such a degree as to insure that each given charge of fresh material fed into the heater, undergoes the same stages 0! in a semlmlast'leiz' and heing' tliereaiter nizlar mass in the Whena phaijzeoi thenfnqp a'stie material first enters the passagefi'rj the heater body llat the completion of the lnje tlonstirolte pi. tha plunger 5. it remains stat onar -wane jth's plunger'witm draws to admit n-e li'c'narge up the ynnqer i. In i-h interval th tfel ses; ber r the-plunger moves again"."thefi'elatli ely' lo' se granular mate rial in the' lfi'assage'i liecomes only partlally plaslicized, due to thlact that'aconsiderable' transfer of heat mus take place between the heated walls of the 'pas'sa''e 'i'lm'd the material'. 310% over. when this heated annular mass oi semiplastic material is fr'n'c'ewlnto the'channels I, by further no iernet'blf the plunger 5, the material is divided td areltitlyely large number of thin streams. 'eabfif 'entifely surmu'ndedfby the heated metal of the 'nose ij'f with' thell'gstiliii that the materialfln e'aeh'ehannel 1 quiekly i aphes a-onditiori of la's'tioity. :r eady for injection into summonses ltp'piasticit'y'is obtainils ihe niate iflal lsu vi dea moafnumbei' r thin stremns ge'a'bh' lat vely small cross s'ection. as compa' ed to'the e 'tire bless-"section pit-he an- While the partic ul r terh ie ratursto be !Fl invdfor eac'h' stag'eneessarilyvaiy'fbr 'differ' mt'iyp's 'f thelfnobla st ib material; generally speaking} 'b'est rsiilt' s*a i'ewbtalned when] the nose 9' containing -'the channels 1 is maintained m. a icmperatur'ifiaterially lower than the temperature wlthinthe b'ody fl'surroundln the an-' milzir passage 6. Such 't'ernperatiiie dlfl'eynces m? primaiilydiletdthe fact that the amount cf heat necessa'r' rt'o't'ransi'orm a single'mas's or elven matei-la l' frp'fii a olcit'o apartiallyplastl sized con'ditiphyi's gi'eatert-han 1he aniriiiritj of heat required to 65mm the desired"'degi'eii of plasticity in "alfeafc'li/ heated material tihatfhas lzer=n subdivided liitbfhini'streams. "T'Howeve'rl'lt has been 'found 'tha'Ffs'olne; the r'lnoplastie" materials are bf uel-i a a'tine asto'req'uire th' irili'im ienance of a 'terfipiatufe arout'i'd theiqhannels I that is substantially e'qu'al to, or even gyeater thanv the temperature maintained m "the body 8 amund the passage By properly setpihg the controllers: 42 and- 43. it is possibletdautoi'natibally rnaintain any'ieiven mate-rial within the ba'rticular tempe'raturelange hlbibs the-desired jnow characteristics, without burning. -'I'herel"ofe. "'each' injection 'st'r'dk Loi 911E pIun'ger' 5 WUrI' SuN i fl a given amount of lhe plasticizedmate'k'liilbelng'forced' into the corperating dies"? while'at the 'same'tlrne a Subslantially'eouai amount of fresh 'matli'ahiglied. V,

- As the -materlalls= ad-vancbd through the salsa-mo ejiii-eotionloil passages oi'ossse ti'rin'al areas" ii. follows that for, a sglv en rate '1 mp mem" of ime manger th .plasticized i o hejnot'ed thatin its the passage hi o'ugfi the apparatus, the pliilstlcl zegl material ounters b lly,v smootmjsubstantially .contlnuiflaces, Wfih qll entliepbsenqe pf pockets $119110 angles wh' 'rfthe inat'eijialimay collect landofi'er resistance to wil ii, (If the entire mass e thematerlalien- This is articularly time w bod :andno'se tem- .a.n'd360", respec- 4 i li'eisame mantfenanpe of. increased .1? aims-i. la wp latspl'lti 1' delf tq handle Th la figures given the conditions a l ven material. 40' and qbyiqusly, theappar tu's hf the pl'esent in Zyentlph isfjusi; as ieflee ve hlppes a'tion-when utilizing, thermoplastic material g equirin'e entirely ifa ii geja'dapted'io i 'the th eii'iflitl eharact eristics or heating "apparatus 01 .chlnes employingtl 1th a e w h fieziea t e. miimwr 55 a givenfriateiial(insures the elllnination of burning oj the matg 'jal elt her ln tli heater or at 't'he dles'." Fiii'thermorefthe adjustability of the pem'iieiatiires that at; automatically maintained within the'heatei makes ithqssiljle foi the same to'ja plasti ized'efq n ragi 'sls" in ,jaassages nf decreasing'erdss-sebtljjn, li'ilthkdii eetloh or movema n; of thkma'terilj sbftljatlfofa given rate 'eil i njeetioniplun 0' trial; .fta mnierm will 11 ove atalgradually creaslp'fij Tate, lwliirjh' will [be gijeatest' wlie'refthe s,ticl'zed lnaterial leaves the hater'hnd 'htei's"the dies. Furthermore.

these passages are formed with smooth contin- 75 uous surfaces, without pockets or angles in which accumulated material might burn or become discolored, due to its failure to move along with the main mass of material. Thus, there is assured an even, measured movement of the entire mass of material in the heater for each operation of the injection plunger. Therefore, when a change is made in the color or character of the thermoplastic material supplied to the machine, there will be no residual deposits of the previously used material, and the number of molded articles exhibiting a mixture of two materials, will be reduced to a minimum. In fact, it has been found that when changing over from one color of material to another. only one or two shots will be required to entirely clear the heater passages of the old material.

While for purposes of illustration the passages for the thermoplastic material have been shown and described as being heated by a hysterisis effect within the surrounding metal, obviously, other means may be employed for applying controlled heat around the passages, without departing from the invention, as set forth in the following claims.

We claim:

1. Heating apparatus for injection molding machines, comprising in combination, a member having a continuous passage therethrough for the movement of heat plasticizable material as a single mass, a plurality of separate channels communicating with said passage for dividing the material into a number of thin streams as it passes therethrough, separate heating means surrounding said passage and channels, and independently operating control devices associated with said heating means for automatically maintaining different temperatures in the vicinity of said passage and channels.

2. Heating apparatus for injection molding macines, comprising in combination, a member providing channels for the movement of heat plasticizable material therethrough, first as a. single mass. and then-sub-divided into thin streams, separate heating means disposed at different portions of said member, and control devices for said heating means for automatically maintaining one portion of the member at a temperature sufilcient to transform a single mass of material from a cold to a partially plasticizod condition, while maintaining another portion of said member at a reduced temperature sufllcient to maintain the desired degree of plasticity n the ready heated material, after it has been divided into thin streams.

3. Heating apparatus for injection molding machines, comprising in combination, a member of heat conducting material having a continuous passage of varying cross-section extending therethrough for the movement of heat plasticizable material, coils surrounding different portions of said member, a source of electrical current, means for independently energizing said coils from said source, to obtain heating within said member in the vicinity of said passage, and means responsive to temperatures within said member at separated points along said passage for automatically controlling the connection and disconnection of said coils to and from said source and thereby maintain a predetermined temperature gradient along said passage.

4. Heating apparatus for injection molding machines, comprising in combination, a member of heat conducting material having a continuous passage of decreasing cross-section extending therethrough for the movement of heat plasticizable material, coils surrounding diflferent portions of said member, a source of electrical current, means for independently energizing said coils from said source, to obtain a heating effect within said member in the vicinity of said passage, thermo-couplcs located in said member at separated points along said passage and controllers responsive to the functioning of said thermo-couples for automatically connecting and disconnecting said coils to and from said source and thereby maintain difierent portions of said member along said passage at difierent predetermined temperatures decreasing in the direction of material flow.

EDWARD S. BIRD. LEON F. MARSH. GRAYDON SMITH. 

